Lead-zinc foams

ABSTRACT

Good quality lead foams are made if the lead is alloyed with zinc, the mixture is treated with CO2 prior to foaming, titanium hydride is used as the foaming agent, the foam is rapidly cooled after formation, and a shallow mold is used. The alloy-hydride mixture can be solidified prior to foaming.

United States Patent [191 Niebylski et al.

n] 3,847,591 1 Nov. 12, 1974 Related US. Application Data [63] Continuation-impart of Ser. No. 155,210, June 21, 1971, Pat. No. 3,790,365, which is a continuation-in-part of Ser. No. 879,915, Nov. 24, 1969, abandoned.

[52] US. Cl 75/20 F, 164/79 [51] Int. Cl 822d 27/00 [58] Field of Search 75/20 F, 29 R; 164/79 [56] References Cited UNITED STATES PATENTS 3,214,265 10/1965 Fiedler v.75/20F 3,305,902 2/1967 Bjorksten 75/20 UX 3,705,030 12/1972 Berry et a1 75/20 F 3,816,952 6/1974 Niebyski et a1 75/20 F FOREIGN PATENTS OR APPLICATIONS Primary Examiner-Andrew R. .luhasz Assistant ExaminerV. K. Rising Attorney, Agent, or FirmDonald L. Johnson; Robert A. Linn [57] ABSTRACT Good quality lead foams are made if the lead is alloyed with zinc, the mixture is treated with CO prior to foaming, titanium hydride is used as the foaming agent, the foam is rapidly cooled after formation, and a shallow mold is used. The al1oy-hydride mixture can be solidified prior to foaming.

1 Claim, No Drawings 12/1965 Canada 75/20 F CROSS-REFERENCE TO RELATED APPLICATIONS This is a continuation-in-part of application Ser. No. 155,210 now US. Pat. No. 3,790,365, issued Feb. 5, 1974, filed June 21, 1971, which in turn is a continuation-in-part of application Ser. No. 879,915, filed Nov. 24, 1969, and now abandoned.

BACKGROUND OF THE INVENTION Lead-zinc alloy has been foamed, and US. Pat. Nos. 2,937,938 and 3,305,902 refer to foaming various metals and alloys thereof. In these disclosures zinc and lead are among the metals mentioned.

Use of carbon dioxide to thicken metal prior to foaming is disclosed in Canadian Pat. No. 912,283.

SUMMARY OF THE INVENTION A preferred embodiment is a process for preparing a foam of a lead-based alloy, said alloy having from about 1.5 weight per cent to about weight per cent zinc, said process comprising substantially saturating a molten mass of said alloy with CO adding with stirring from about 2 g to about 5 g of Til-I per 100 gram portion of lead while maintaining the temperature of the mass to be foamed below about 410C., subsequently raising the temperature to from about 420C. to about 475C. to foam said mass, and then quickly cooling the foam thereby produced below its solidification temperature.

DESCRIPTION OF PREFERRED EMBODIMENTS Preferably the lead contains from about 1 weight per cent to about weight per cent or higher, and more preferably from about 1.5 weight per cent to about 6 weight per cent zinc. In a preferred embodiment the metal mass consists essentially of lead and zinc and has can be used. Preferably, the CO is added as solid CO but gaseous CO can be used as well. Addition of solid CO can appreciably lower the metal temperature. Thus, we add CO at a rate at which solidification doesnt take place. Any convenient rate which avoids solidification can be used.

The time of CO addition isnt critical; and usually is complete in from one-half minute to 5 minutes. To some extent, the time depends on size of the mass to be foamed. Stirring while adding assists uniform mixing of CO and metal and is preferred. Other means of agitation can be used.

If CO is added until the metal is saturated or nearly so, and at a temperature above the foaming temperature, the melt can be saturated or substantially saturated with CO at foaming temperature. The amount of foaming agent used depends in part on the density of foam desired. Of the hydride foaming agents, Til-l is preferred. For each gram portion .of lead to be foamed, preferably from about 2 to about 5 grams, more preferably from 3 to 5 grams of TiH is used. In a preferred embodiment, for foams of about 1.0 per cent density, from 4.5 to 5 grams (per 100 gram portion of lead) is employed.

The hydride is added to the molten metal mass at a temperature below about 410C. Preferably the mixture is at about 400C. when the hydride is added.

Stirring or other means of agitation which enhances mixing of the hydride in the metal mass are preferentially used when adding the foaming agent.

After introducing the hydride into the mass to be foamed, the mass temperature is raised to a foaming temperature of from about 420C. to about 475C. This decomposes the foaming agent and foams the metal.

After the desired degree of foaming has been reached, the foamed mass is quickly cooled. This can be accomplished by quenching with tap water, or with dry ice, or with a chilled copper plate heat sink, or other similar technique.

Conducting the foaming in a shallow vessel, say up to about 5 inches in height, enhances the ability to rapidly cool the foam. Thus, this expedient is preferred.

EXAMPLE A procedure for producing a high quality foam is as follows:

Add 5 per cent zinc to chemically pure Pb; raise the melt temperature to 500C. and add CO (dry ice) until no more CO can be added. Then at 400C, add approximately 5 g Til-l l 100 g Pb with vigorous stirring. Cast into a preheated mold (470C.) and place in an oven at that temperature for 3-5 minutes. After that time, the Pb foam is quenched in the oven with dry ice or H2O before moving so as to prevent any foam 2 9 59.L 9u?1?$: s. 7

Similar results are obtained when the amount of zinc is from 1.5 to 5.0 per cent,

the CO is added at from 475 to 525C,

the Til-I is added at from 400 to 410C.,

the amount ofTiH is from 2 to 5 g per 100 g of lead,

the foaming temperature is from 420 to 475C., and

' Compressive Strength Sample No. (psi) Density (pcf) All compressive values were taken at 10 per cent compression of the 0.75 inch thickness. There was no peaking in the laod-deflection curve, only a change in slope at about 5 per cent compression. The Pb samples showed no crumbling at up to 30 percent compression.

The data showsthat th e lead foams have strengths of Good quality foams have been or no drainage.

Tests have been conducted to show feasibility of use of a lead foam produced by the process of the above exproduced having little ample as an acoustical material for sound deadening,

dampening or isolation purposes. Measurements were made in a Bruel and' lzj a er acoustic use on a9.4 cm specimen at 250, 500, 1,000 and 2,000 Hz. The specimens were backed by a steel plate. The method of measurement is that described in the American Society for Testing and Materials Standard Method of Test for Impedance and Absorption of Acoustical Materials by the Tube Method, ASTM Designation C384-58. Results of Test The a,,s are the absorption coefficients at normal in cidence. They mean the fraction of the incident sound power absorbed when sound impinges perpendicularly on the material. The a s are approximate coefficients which might be obtained by a large scale test in the reverberation room where sound impinges on the material at all angles.

Normal Approximate Random H Coefficients, Coefficients. of,

Foamed 250 .09 .17 Pb-5 per cent 500 .l5 .28

Zn Alloy 1000 .19 .34 2000 .06 .12 Lead Sheet- 250 .05 .l l Urethane Foam 500 .04 .05 1000 .04 .05 Composite 2000 .07 .13

These data indicate foamed lead is better than the sheet lead-urethane foam composite in the range 500l,000 Hz whereas the materials are nearly equal in absorption at the high and low frequency ranges.

Similar results are obtained on foams having a density from 68 to 101 pcf.

The sheet lead-urethane foam composite used in the above test for comparison was a commercially available acoustical material.

If desired, the foams of this invention can be bonded to urethane or Polyvinyl chloride foams to form an acoustical composite.

The foams of this invention can be used as shock absorbing materials in passenger or freight compartments of vehicles to prevent or lessen damage on impact.

We claim:

1. Process for preparing a metal foam from a lead based metal having from 1.5 to 5 weight per cent zinc, said process comprising substantially saturating a molten mass of said metal with CO subsequently adding with stirring from 1.5 to 5 grams of Til-I per gram portion of Pb while maintaining the temperature of the mass below about 410C., subsequently raising the temperature to from about 420C. to about 475C. to foam said mass, and quickly cooling the foam thereby produced below its solidification temperature to form a set cellular product. 

1. PROCESS FOR PREPARING A METAL FOAM FROM A LEAD BASED METAL HAVING FROM 1.5 TO 5 WEIGHT PER CENT ZINC, SAID PROCESS COMPRISING SUBSTANTIALLY SATURATING A MOLTEN MASS OF SAID METAL WITH CO2, SUBSEQUENTLY ADDING WITH STIRRING FROM 1.5 TO 5 GRAMS OF TIH2 PER 100 GRAM PORTION OF PB WHILE MAINTAINING THE TEMPERATURE OF THE MASS BELOW ABOUT 410*C., SUBSEQUENTLY RISING THE TEMPERATURE TO FROM ABOUT 420*C. TO ABOUT 475*C. TO FOAM SAID MASS, AND QUICKLY COOLING THE FOAM THEREBY PRODUCED BELOW ITS SOLIDIFICATION TEMPERATURE TO FORM A SET CELLULAR PRODUCT. 